What is molecular weight?

Molecular Weight :  The molecular weight of a molecule refers to the sum of the atomic weights of all the atoms making up the molecule. The gram molecular weight of a substance is the molecular weight expressed in grams. For example, the atomic weight of oxygen is 16, and that of hydrogen is 1, so one gram molecular weight, or mole, of water equals 18 grams.

Since one mole of any substance contains the same number of molecules, 6.022 x 1023, the concept is useful in describing chemical reactions. In biological experiments, the concentration of a solution, that is, the amount of solute dissolved in the solvent, is usually expressed in terms of molarity. A molar (1M) solution contains a mole of solute in 1 liter of solution. Note that by convention, "mole" is abbreviated as "mol."